1. Field of the Invention
This invention relates generally to receiver circuit architecture in a wireless portable communication device. More particularly, the invention relates to channel estimation in a wideband code division multiple access (WCDMA) communication system.
2. Related Art
With the increasing availability of efficient, low cost electronic modules, mobile communication systems are becoming more and more widespread. For example, there are many variations of communication schemes in which various frequencies, transmission schemes, modulation techniques and communication protocols are used to provide two-way voice and data communications in a handheld, telephone-like communication handset. The different modulation and transmission schemes each have advantages and disadvantages.
As these mobile communication systems continue to evolve, so do the operating requirements. Current and future mobile communication systems must be able to operate under diverse and harsh operating conditions. For example, current and future communication systems must be able to reliably operate in what is referred to as a “high speed” environment. A high speed environment is one in which the portable communication device is moving at a high rate of speed with respect to the base station with which it is communication. A portable communication device operating in a high speed train, where speeds approach and exceed 300 kilometers per hour (Km/h), is one example of such a high speed environment. A moving vehicle causes the signal received by the portable communication device (i.e., the handset, or mobile) to fade, whereby the signal amplitude and phase varies in time in addition to the amplitude and phase variations imposed by the modulation of the signal.
In a code division multiple access (CDMA) communication environment, a pair of pilot channels are provided so that the handset can estimate channel parameters and make corrections to the traffic channel based on the parameters of the pilot channel. Accurately characterizing the amplitude and phase reference of the pilot channel, referred to in CDMA as “channel estimation,” is vital to accurately demodulate the traffic channel and increasingly important to performance under the new 3G (wideband CDMA, or WCDMA) standard. In WCDMA, two pilot channels from two diverse antennas (referred to as a “diversity” antenna system) are transmitted simultaneously. However, the complexity and delay associated with estimating the channel parameters of the pilot signal in a high speed environment makes accurately demodulating the traffic channel a resource intensive operation.
Therefore, it would be desirable to have a way to efficiently estimate the channel parameters in a WCDMA communication system.